The present invention relates to a method and a device for regulating the boost pressure of an internal combustion engine having an exhaust gas turbocharger whose turbine, which is located in the exhaust gas channel of the internal combustion engine, has an adjustable geometry, with the regulation of the boost pressure occurring via an adjustment of the turbine geometry.
As it is provided in, for example, German Published Patent Application No. 41 07 693 or European Published Patent Application No. 04 54 943, boost pressure regulation is typically performed by a controller producing a manipulated variable as a function of the deviation between a specified boost pressure and an actual boost pressure. This manipulated variable is used either for controlling a valve in a bypass which bypasses the turbine of the turbocharger in the exhaust gas channel (see German Published Patent Application No. 41 07 693) or for controlling the adjustable turbine guide vanes of a turbine having variable geometry (see European Published Patent Application No. 04 54 943).
Increasingly higher requirements are placed on, engines in regard to exhaust gas and consumption characteristics. An exhaust gas turbocharger having variable turbine geometry allows an adjustment to the current engine operating point through adjustment of the turbine guide vanes. With this technique, a delayed response of the exhaust gas turbocharger (turbo lag) can be reduced and the efficiency of the engine can be improved at the same time. Overshoots of the boost pressure, which mechanically stress the turbocharger very strongly, often occur during acceleration operations. In addition, excessive closing of the variable turbine geometry in the acceleration phase can result in an unwanted high exhaust gas back pressure, which negatively influences the dynamic response and efficiency of the engine.
The present invention therefore has as its object the provision of a method and a device for boost pressure regulation of the type cited initially which ensure that the boost pressure follows the course of the desired boost pressure specified value as rapidly as possible in the case of an alternating load, with an overshoot of the boost pressure specified value being avoided to protect the exhaust gas turbocharger from unnecessarily high loads.
The object cited is achieved in that a manipulated variable for the turbine geometry is determined as a function of the exhaust gas back pressure prevailing in the exhaust gas channel upstream from the turbine. The exhaust gas back pressure responds significantly faster than the boost pressure to changed behavior of the controlled systemxe2x80x94e.g., speed change, alternating load, change in exhaust gas recirculationxe2x80x94or to malfunctions, e.g., in the servo-system. Therefore, if the exhaust gas back pressure is used according to the present invention to derive a manipulated variable, a very rapid response of the boost pressure regulation to a change in the preset specified boost pressure is achieved.
An advantageous refinement of the method according to the present invention and the device according to the present invention is that a specified exhaust gas back pressure is determined by a first controller from the deviation between a specified boost pressure and an actual boost pressure, and the manipulated variable for the turbine geometry is derived by a second controller from the deviation between the specified exhaust gas back pressure and a measured or estimated actual exhaust gas back pressure.